Material feeding apparatus with capacitive control



2 Sheets-Sheet 1 H. J. STEEL MATERIAL FEEDING APPARATUS WITH CAPACITIVECONTROL mz z om l u Nq on fi m mm C 3 QM 93 N R E Q r 1 E0 5 om N2 mmmnwmww Dec. 10, 1968 Filed Jan. 31, 1967 .22: wmomm H. J. STEEL Dec. 10,1968 MATERIAL FEEDING APPARATUS WITH CAPAGITIVE CONTROL Filed Jan. 31.,1967 2 Sheets-Sheet 2 NdE United States Patent 3,415,417 MATERIALFEEDING APPARATUS WITH a CAPACITIVE CONTROL Henry John Steel, Malvern,England, assignor to Autopack Limited, Malvern Link, Worcestershire,England Filed Jan. 31, 1967, Ser. No. 612,942 Claims priority,application Great Britain, Jan. 31, 1966, 4,097/66 1 Claim. (Cl. 222-55)ABSTRACT OF THE DISCLOSURE A pair of electro-magnetic'ally drivenvibratory feedersare arranged in series, feeding from a hopper to aweigh pan. A capacitive depth control sensitive to the depth of materialon the second conveyor is arranged of material on the second conveyor isarranged to control the amplitude of vibration of the first conveyor.

This invention relates to material feeding apparatus and has as anobject to provide such apparatus in a convenient form.

Material feeding apparatus in accordance with the invention comprises afirst conveyor, first drive means for driving said first conveyor toadvance material along said first conveyor, a second conveyor arrangedto receive material delivered by said first conveyor, second drive meansfor driving said second conveyor to advance material along said secondconveyor, means sensitive to the depth of material on the secondconveyor and control means operable by said depth sensitive means forcontrolling said first drive means to vary the rate of delivery ofmaterial by the first conveyor so as to tend to keep the depth ofmaterial on the second conveyor constant.

Reference is now made to the accompanying drawings in which:

FIGURE 1 is a diagrammatic view illustrating an example of theinvention,

FIGURE 2 is an elevation of an embodiment of the invention, and

FIGURE 3 is an electrical circuit diagram showing the full electricalarrangement used in the example of the invention described.

Referring to the drawings, material feeding apparatus is required tofeed material from a hopper to a weighing apparatus 11. The weighingapparatus 11 is provided with any convenient means 12 which may be inthe form of a switch, for arresting feed of material after apredetermined weight has been fed.

In the example described, the feeding apparatus is of the vibratorytype, and in fact consists of two vibratory trays 13, 14, the first 13,of which receives material from the hopper 10 and delivers it to thesecond tray 14 which in turn delivers the material to the weighingmechanism 11.

A tray 13 is supported on a first body 15 through the intermediary of apivoted link 16, and a leaf spring 17. The arrangement of the leafspring 17 is such that when the tray is in repose, as shown, the leafspring 17 and the link 16 extend in parallel directions inclined to thetray 13. Thus reciprocatory movement of the tray 13 will be accompaniedby rising and falling of the tray. As the tray is advanced it rises andas the tray retreats in the direction opposite that in which it isdesired to feed the material, the tray falls. Secured to the tray is afurther magnetic armature 18 which co-acts with a coil 19 to drive thetray. The body 15 is carried on springs 20 on a base 21.

The tray 14 is supported in an essentially similar manner on a body 22carried by springs 23 on the base 21. An armature 24 is secured to theunderside of the tray 14, and co-acts with a coil 25. The tray 14 is ata lower level than the tray 13, and the two trays overlap so thatmaterial falling from the tray 13 is caught by the tray 14.

The coil 25 is supplied with power from an AC. source 26 through theintermediary of a series circuit consisting of the switch 12, a variableresistor 27 and a diode 28. Whenever the switch 12 is closed, therefore,current will flow through the coil 25 during alternate half cycles ofthe supply, the magnitude of the current being dependent upon thesetting of the variable resistor 27. When the switch 12 is opened by theweighing mechanism, the tray 14 will come to rest.

In order to ensure that the material which falls from the tray 14 afterthe switch 12 has been opened is kept constant, it is desirable toensure that the depth of material on the tray 14 is also kept constant.This is effected by controlling the amplitude of the vibrations of thefirst tray 13 in accordance with the measured depth of material on thesecond tray 14. To this end. there is provided means sensitive to thedepth of material on said second tray. Such means consists of acapacitive probe plate 29 supported over the tray 14, which is earthed.The combination of the probe 29 and the earthed tray 14 are representedin FIGURE 3 by the variable capacitor 30,

As shown in FIGURE 2, the probe plate 29 is adjustably mounted over thetray 14, so that adjustment of the depth of material on the tray 14 canbe effected by varying the height of the probe plate 29. The probe plateis suspended by a rod 31 from a unit 32 which includes the circuitelements immediately associated with the probe plate 29. The unit 32 isin turn supported on a stand 33 on the base 21, the upper end of thestrand 33 is constituted by a vertical screw 34 on which a bracket 35 ismounted by means of upper and lower adjusting screws 36, 37, a rod 38secured to the unit 32 is screw-threaded and is similarly adjustablerelative to the bracket 35 by means of nuts 39, 40.

Turning now to FIGURE 3, it will be seen that the power supply for theunit 32 is derived from the AG. source 26 through the intermediary of atransformer 41. The secondary winding of this transformer has a centretapping which is earthed. The respective ends of the secondary windingare interconnected by a capacitor 42 and are connected respectively tothe anodes of a pair of diodes 43, 44, the cathodes of these two diodesare connected together and are earthed through a capacitor 45. Inaddition, the cathodes are connected through a resistor 46 and a pair ofZener diodes 47, 48 in series to earth, the anode of the Zener diode 48being connected to earth, and the cathode of the Zener diode 47 beingconnected to the resistor 46. In effect therefore, the potential of thecathode of the diode 47 remains at a substantially constant level at alltimes. The input terminal 49 of the unit 32 is connected to the cathodeof diode 47.

The unit 32 includes a high frequency oscillator including an n-p-ntransistor 50. The base of this transistor is connected to one end ofone of a pair of primary windings 51, 52 of a transformer 53, the otherend of primary winding 51 is connected through a resistor 54 to earth,the resistor 54 being bridged by a capacitor 55. The collector oftransistor is connected to one end of the other primary winding 52, theother end of which is connected through a resistor 56 to the terminal49. The emitter of transistor 50 is connected to earth through aresistor 57. The said other ends of the primary windings 51, 52 areinterconnected by a resistor 53, and the series circuit constituted bythe resistors 54, 58 is bridged by a capacitor 59.

The output of the high frequency oscillator is taken from the secondarywinding 60 of the transformer 53. This winding is bridged by a pair ofcapacitors 61, 62 in series, with their interconnections earthed. Thusthe secondary winding 60 provides at its ends two output voltages whichare equal in amplitude but of opposite phase relative to earth. Thevariable capacitors (which is in fact constituted by the probe plate 29and the tray 14) has one plate connected to earth and the other plateconnected to one end of the Winding through the intermediary of acapacitance 63 and a variable capacitance 64 in series. The capacitors30 thus forms one arm of a capacitive potential divider, the other armof which is constituted by the capacitors 63, 64 in series. Theamplitude of the signal at the connection '65 (which is connected to theprobe plate 29) will therefore vary in accordance with the capacitancefor the time being of the capacitors 30. The interconnection 65 isconnected to the input terminal 66 of an A.C. amplifier through acapacitor 67 of very low capacitance. In order to prevent high standingvoltages from being applied to the input terminal 66, this is connectedthrough a capacitor 68 and a variable capacitor 69 in series to theother end of the winding 60 so as to apply a signal of opposite phase tothe terminal '66. By suitable adjustment of the capacitor 69 it cantherefore be arranged that the changes in the amplitude of the signal atterminal 66 are not small compared with the standing voltage there.

The terminal 66 is connected to the base of an n-p-n transistor 70 whichis also connected through a resistor 71 to the terminal 49, and througha resistor 72 to earth. A resistor 73 connects the emitter of transistor70 to earth. The collector of transistor 70 is connected through aparallel tuned circuit to the terminal 49, the tuned circuit consistingof the primary winding of a variable transformer 74, and a capacitor 75.

The secondary winding of the transformer 74 has one end earthed, and theother end connected to the anode of .a diode 76, the cathode of which isconnected to one end of a potentiometer 77 earthed at the other end. Thepotentiometer is bridged by a capacitor 78. The variable point of thepotentiometer is connected to the input terminal 79 of a control circuitfor controlling the current to the coil 19.

The control circuit is operated by a pulsed D.C. supply derived from thetransformer 41. It will be seen that the anode of the diode 44 isconnected to the anode of a diode 80, the cathode of which is connectedthrough a resistor 81 to the cathode of a Zener diode 82. The anode ofthe Zener diode 82 is earthed. At the cathode of the Zener diode 82therefore, D.C. pulses in synchronism with alternate half cycles of theA.C. supply. A potential divider consisting of resistors 83, 84 isconnected across the Zener diode 82 and the interconnection of theresistors 83, 84 is connected to one end of the primary winding 85 of atransformer 86, the other end of this winding 85 is connected to the:base of an n-p-n transistor 87. The collector of transistor 87 isconnected to one end of one of the secondary windings 88 of thetransformer 86, the other end of winding 88 being connected to thecathode of the Zener diode 82. The collector of transistor 87 is alsoconnected to the above of a diode 89 having its cathode connected to thecathode of Zener diode 82. The resistors 83, 84, the transformer 86, thetransistor 87 and the diode 89 form a blocking oscillator whichoscillates when a signal is applied to the emitter of transistor 87.

This signal is applied by means of an n-p-n transistor 90 with itsemitter connected via a resistance 91 to earth, and its collectorconnected through a capacitor 92 to the cathode of the Zener diode 82and to the emitter of transistor 87. Thus, in use, the blockingoscillator will oscillate during alternate half cycles of the supplycommencing a variable time after the commencement of the appropriatehalf cycles. The time delay depends upon the DC. signal applied to thebase of the transistor 90. When a transistor 90 is hard-on the capacitor92 will be charged rapidly and oscillation will commence early. When, onthe other hand, the transistor 90 has only a small signal applied to itsbase, there will be a comparatively long delay before oscillationcommences.

The DC. signal at terminal 79 of the probe unit 32 is amplified andapplied to the base of transistor 90. The amplifier consists of twotransistors 93, 94 having their emitters connected to earth through acommon resistance 95. The base of transistor 94 is connected to terminal79, and its collector is connected to the cathode of the Zener diode 82through a resistor 96. The collector of transistor 93 is connected tothe cathode of Zener diode 82 by a resistor 97, and directly to the baseof transistor 90. The base of. transistor 93 is held at a substantiallysteady potential derived from a potential divider 98, across theresistor 46. The mid-point of this divider is connected to the base oftransistor 93 through a resistor 99 and the base of resistor 93 alsoreceives a bias from resistors 100, 101 in parallel and connected toearth.

The coil 19 for driving the first tray 13 is connected across the A.C.source in series with a silicon controlled rectifier 102. Thegate-cathode circuit of this silicon controlled rectifier consists of awinding 103 of the transformer 86, and a resistor 104 in series. Acapacitor 105 interconnects the anode and cathode of the rectifier 102.

It will be appreciated that the capacitance of the probe capacitor 30will vary in accordance with the depth of material on the tray 14. Itscapacitance will be at a minimum when the tray is empty, and will riseirrespective of whether the material on the tray is conductive ordielectric, the di-electric constant for most solids being considerablyin excess of unity. Thus, the amplitude of the A.C. signal at terminal66 decreases as the level of material on the tray 14 increases. Thus theDC. signal applied to the output terminal 79 of the probe devicedecreases as the level rises. As the signal at terminal 79 decreases,the current flowing through resistor decreases, thereby creating asmaller voltage drop across the resistor 95. The transistor 93 isthereby rendered more conductive, and a considerable drop in thepotential at the base of the resistor 90 is therefore experienced. Thisin turn increases the delay at the start of each alternate half cycle ofthe A.C. supply before the blocking oscillator commences itsoscillations, and causes firing of the silicon controlled rectifier 102.Thus, as the level of material on the tray increases the power deliveredto the coil 19 decreases and thus the amplitude of the vibration of thetray 30 is likewise decreased. A stable equilibrium condition exists inwhich changes in depth of the material on the tray 14 are rapidlyconnected by variation of the amplitude of vibration of the tray 30. Therate at which material is fed for a given material and arrangement ofthe probe 29 is determined solely by the variable resistor 27 in thecircuit of the coil 25. As the amplitude of vibration of the tray 14 isvaried, by adjustment of resistor 27, the amplitude of vibration of thetray 13 will he automatically varied to keep the depth of material onthe tray 14 constant. The depth of material can, however, be varied byadjusting the height of the probe plate 29, or, alternatively, adjustingcapacitor 64 or 69.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. Material feeding apparatus comprising a first conveyor and firstdrive means therefor, said first conveyor comprising an elongated traymounted for reciprocatory movement and said first drive means comprisingan electro-magnet having a coil and an armature mounted respectively onsaid tray and a base on which said tray is supported, a second conveyorarranged to receive material from said first conveyor and second drivemeans for driving said second conveyor to advance material along suchsecond conveyor, a capacitive probe plate supported over said secondconveyor and connected in an A.C. control circuit for saidelectro-rnagnet, said A.C. control circuit comprising a semiconductorcontrolled rectifier having an anode-cathode circuit in series with saidcoil and also having a gate to Which pulses are delivered by said A.C.control circuit to initiate conduction of said semiconductor controlledrectifier, said capacitive probe plate and the second conveyor forming,in combination, a capacitor which is part of an A.C. potential divider,said A.C. control circuit delivering a conduction initiating pulse tosaid gate at an instant after the commencement of each conductive halfcycle of said semiconductor controlled rectifier determined by themagnitude of an A.C. signal generated by said A.C. potential dividerdependent on the dept-h of material on said second conveyor, whereby therate of delivery of material to the second conveyor by the firstconveyor is varied to keep a depth of material on the second conveyorconstant.

References Cited UNITED STATES PATENTS 1,889,663 11/1932 Ilyus 222-521,460,573 7/1923 Church et al. 222-55 2,909,303 10/1959 Henderson et a1.222-52 X 3,062,355 11/1962 Sawada 222-55 3,149,650 9/1964 Horst 222-52ROBERT B. REEVES, Primary Examiner. H. S. LANE, Assistant Examiner.

US. Cl. X.R.

